Mass spectrometer electrostatic analysers



June29, 1965 E. WILLDIG 3,192,384

MASS SPECTROMETER ELECTROSTATIC ANALYSERS Filed Sept. 11, 1962 INVENTOR:

Ed Ward W l'lldig ATTORNEY by suitable connecting ducts.

United States Patent 3,192,384 MASS SPECTROMETER ELECTRGSTATIC ANALYSERS Edward Willdig, Stretford, England, assiguor to Associated Electrical Industries Limited, London, England, a British company Filed Sept. 11, 1962, Ser. No. 222,840 Claims priority, application GreatBritain, Sept. 15, 1961,

33,217 61 4 Claims. (Cl. 250-419) The present invention relates to mass spectrometer electrostatic analysers.

One form of double focusing mass spectrometer includes an ion source, an electrostatic analyser, a magnetic analyser and a collector. The ions produced in the ion source are passed through the electrostatic analyser in which each ion is deflected in accordance with its energy level, and through the magnetic analyser in which each ion is deflected in accordance with its mass/charge ratio and its energy. The ions after deflection are received by the collector.

The electrostatic analyser comprises two electrostatic deflecting plates between which the ion beam passes. A potential difference is applied between the plates and the resultant electric field deflects the ions. In order to ensure adequate performance of the analyser it is essential that the deflecting plates should be spaced apart in a predetermined manner and this spacing should remain constant in spite of any changes in the temperature of the analyser.

' The object of the present invention is to provide an improved form of massspectrometer electrostatic analyser.

According to the present invention a mass spectrometer electrostatic analyser comprises a chamber adapted to be evacuated, two superposed electrostatic deflecting plates located within said chamber and defining a gap between their adjacent surfaces for the passage of an ion beam, means for connecting said two deflecting plates respectively to suitable sources of potential so as to produce an electric field between said two plates, and means for supporting the upper deflecting plate from the lower deflecting plate so as to prevent relative movement between the adjacent central regions of the deflecting plates but to permit relative longitudinal movement between the remaining adjacent regions of the deflecting plates.

Preferably the. supporting means comprises a plurality of spacer members which abut against co-operating surfaces on the two deflecting plates so as to space the two deflecting plates apart and restrict the relative movement between the plates as required.

The lower deflecting plate is preferably supported within the chamber so as to permit relative movement between the lower plate and the chamber.

By supporting the deflecting plates as above, relative movement between the plates due to thermal expansion takes place with the minimum alteration in the width of the gap between the plates.

In order that the invention may be more readily understood reference will now be made to the accompanying drawings in which:

are connected to one evacuating system or to separate evacuating systems and are joined together as illustrated Ions produced in the ion source 1 from a sample to be analysed pass through the electrostatic analyser 2 and the magnetic analyser 3 in succession and are finally received by the collector 4.

FIG. 2 illustrates the electrostatic analyser in greater detail. The analyser comprises a chamber 11 adapted to be evacuated through a duct 12 and formed with an inlet aperture 13 and an outlet aperture 14. The inlet aperture 13 is adapted to be connected to a duct connecting with an ion source and two pairs of half plates 15, 16 are located adjacent to the inlet aperture in order to deflect a beam of ions from the ion source as required. A monitor collector device 17 is located adjacent to the outlet aperture 14, in order to monitor the beam of ions as it leaves the electrostatic analyser.

The chamber 11 is conveniently formed from mild steel suitably plated with a nickel alloy.

Within the chamber 11 are supported two deflecting plates 13, 19, conveniently made of stainless steel and drilled in order to reduce their weight. The deflecting plates are formed respectively with cylindrical surfaces 21, 22, and the plates are located so that these cylindrical surfaces are co-axial and hence are spaced apart by a constant gap. Each of the cylindrical surfaces is very smooth. The analyser is mounted in a vertical plane so that the deflecting plates are superposed.

The lower deflecting plate 18 is supported on two quartz plates 23, 24 which are themselves supported on two members 25, 26 shaped so as to form heat chokes. The plate 18 is formed with a first cylindrical recess 27 into which a first quartz dowel 28 projecting through the plate 23 fits tightly. The plate 18 is also formed with a second recess 29 into which a second quartz dowel 30 fits loosely in onedirection so that relative longitudinal movement between the plate 18 andthe supports is permitted in the region of the second recess 29 but is not permitted in the region of the first recess 27. Hence if the plate 18 expands with an increase in temperature longitudinal movement relative to the chamber is permitted.

The upper deflecting plate 19 is supported from the lower plate 18 on six quartz spacers, each of which conveniently comprises a cylindrical member. The three spacers 31, 32 and 33 visible in FIG. 2 are supported in V-shaped recesses in the top surfaces of three lugs 34, 35 and 36v attached to the lower plate. The outer two spacers 31, 33 abut respectively against the flat lower surfaces of lugs 37 and 39 attached to the upper plate 19, and the middle spacer 32 is located in V-shaped recess in the lower surface of another lug 38 attached to the upper plate 19. It will be appreciated that the plates 18, 19 are formed with similar lugs on the sides not illustrated in FIG. 2 and corresponding quartz spacers are located in a similar manner so that the upper plate 19 is supported from the lower plate 18 by six spacers.

Since the middle spacers are located in V-shaped recesses in the surfaces of the lugs on both the plates, no relative longitudinal movement between the adjacent central regions of the two plates is permitted, but since the outer two spacers abut against flat surfaces on the lugs attached to the upper plate, relative longitudinal movement between the adjacent ends of the plates is permitted.

With such an arrangement of supports for the two deflecting plates, thermal expansion of the plates is permitted but the relative movement between the plates is kept to a minimum. By this arrangement variation in the width of the gap between the surfaces 21, 22 is reduced to a minimum and possibility of distortion is mini mized.

[he plates 18, 19 are adapted to be connected respectively to suitable sources of potential so that a beam of ions entering the analyser is deflected as it passes through the gap between the surfaces 21, 22 and passes out able-electrical connection to the field correcting plates" 43, 44 and that these connections will pass through the Wall of the chamber 11 and will be insulated'therefrom, but these have been omitted from the drawing for clarity. The spacer-members 31, 32, 33 may alternatively be made of any material with a low co-eflicient of thermal expansion such as glass or ceramic.

By constructing the electrostatic analyser in accordance with the invention when the components expand due to an increase in temperature, during baking for example, the components move relatively so that they are not distorted and so that the shape of the space between the two deflecting plates does not substantially alter. When the components cool down again they return to their original positions. It will be appreciated that the deflecting plates are not clamped together but are maintained in Position by gravitational forces.

What I claim is: a

1. A mass spectrometer electrostatic analyser comprising a chamber adapted to be evacuated, two superposed electrostatic deflecting plates located within said chamber and defining a gap between their adjacent surfaces for the passage of an ion beam, means for connecting said deflecting plates respectively to suitable sources of potential so asto produces'an electric field between said plates, and means for supporting the, upper deflect-ing plate at intermediate central portions of the ends of the plates from the lower deflecting plate so as to prevent relative movement between the adjacent: central regions of the deflecting plates and additional spacing means between the plates adjacent the ends thereof to permit relative longitudinal movement between the remaining adjacent regions of the deflecting plates.

21. A mass, spectrometer electrostatic analyser comprising a chamber adapted to be evacuated, two superposed electrostatic deflecting plates located within said chamber and defining a gap between their adjacent surfaces for the passage ,of an ion beam, means for connecting said deflecting plates respectively to suitable sources of potential so as to. produce an electric field between said plates, interconnecting means between the between the adjacent central regions of the, deflecting plates but to permit relative longitudinal movement between the remaining adjacent regions of the deflecting plates,-.and means for securing against movement only one end portion of the lower deflecting plate to said chamber so as to permitrelative movement between the rest of said lower deflecting plate and said chamber.

3. A mass spectrometer electrostatic analyser comprising a chamber adapted to be evacuated, two superposed electrostatic deflecting'plates located within said chamber and defining a gap between .their adjacent surfaces for the passage of an ion beam, means for connecting said deflecting plates respectively to suitabletsources of potential so as to produce an electric field between said plates, and a plurality of spacer members abutting against co-operating surfaces on said two deflecting plates so as Y to'support the upper deflecting plate from the lower defleeting plate in sucha Way, as to prevent relative movement between the adjacent central regions of the two deflecting plates but to permit relative longitudinal move ment between the remaining adjacent regions of the deflecting plates. a

4. A mass spectrometer electrostatic analyser comprising a chamberadapted totbe evacuated, two superposed electrostatic deflecting plates located within said chamber and defining a gap .between their adajcent surfaces I for the passage of ,an ion beam, means for connecting said deflecting plates respectively to suitable sources of potential so as to produce an electric field between said plates, and three pairs of spacer members'arranged along the. gap between the deflecting plates and abutting against co-operating surfaces on said deflecting plates sothat the upper deflecting plate is supported from the lowed deflecting plate, the, middle pair of spacer members being located adjacent to the middle of said deflecting plates; and fixed relative to the two deflecting plates so as to prevent relative movement between the adjacent central regions of the deflecting plates, and the outer pairs of spacer members being fixed relative to one deflecting plate andfree to move longitudinally relative to the other deflecting plate'so as to permit relative longitudinal move ment between the remaining adjacent regions of the deflecting plates.

RALPH G. NILSON, Primary Examiner. 

1. A MASS SPECTROMER ELECTROSTATIC ANALYSER COMPRISING A CHAMBER ADAPTED TO BE EVACUATED, TWO SUPERPOSED ELECTROSTATIC DEFLECTING PLATES LOCATED WITHIN SAID CHAMBER AND DEFINING A GAP BETWEEN THEIR ADJACENT SURFACES FOR THE PASSAGE OF AN ION BEAM, MEANS FOR CONNECTING SAID DEFLECTING PLATES RESPECTIVELY TO SUITABLE SOURCES OF POTENTIAL SO AS TO PRODUCE AN ELECTRIC FIELD BETWEEN SAID PLATES, AND MEANS FOR SUPPORTING THE UPPER DEFLECTING PLATE AT INTERMEDIATE CENTRAL PORTIONS OF THE ENDS OF THE PLATES FROM THE LOWER DEFLECTING PLATE SO AS TO PREVENT RELATIVE MOVEMENT BETWEEN THE ADJACENT CENTRAL REGIONS OF THE DEFLECTING PLATES AND ADDITIONAL SPACING MEANS BETWEEN THE PLATES ADJACENT THE ENDS THEREOF TO PERMIT RELATIVE LONGITUDINAL MOVEMENT BETWEEN THE REMAINING ADJACENT REGIONS OF THE DEFLECTING PLATES. 